Real Hot Stuff has just sent me a replacement for my first Supercard that has exactly the same problem as the one I returned: the supercapacitor (it's not a "battery") will not hold a charge and, as a result, the contents of the SRAM are lost when the GBA or DS is turned off.

The odds of getting two bad carts in a row is virtually nil unless there was an entire string of bad carts produced, probably because an entire batch of the supercpacitors used was bad. This would not be caught with the kind of self-test they likely perform at the factory, the L+R shoulder button initiated one, which cannot reveal an inoperative supercapacitor.

As I stated at PH, it's likely that you're simply unaware that that's the way Supercards work. Are you aware of the button combination needed to save the SRAM to the *.sav file (GBA files only, not DS)?